When people with active pulmonary TB cough, sneeze, speak, sing, or spit, they expel infectious aerosol droplets 0.5 to 5.0 µm in diameter. A single sneeze can release up to 40,000 droplets. Each one of these droplets may transmit the disease, since the infectious dose of tuberculosis is very low (the inhalation of fewer than 10 bacteria may cause an infection).
BTW, America is full of people with some degree of natural immunity to TB ~ but we also have some people who have a tendency to die from it in record time.
If you read through the information on the net regarding immunity there's not a whole lot of studies been done on that side of things ~ probably because we've had antibiotics that work.